The invention relates to a synchronous motor with an electronic control device for adjusting devices in motor vehicles, in particular for adjusting devices with trap protection and/or limitation of excess force, and to a method of controlling the motor-drive unit of the adjusting device. The drive unit according to the invention may be used particularly advantageously in conjunction with an electrically operated window regulator or a sliding roof.
A generic electronically controlled drive unit is known from EP 0 482 040 B1. It consists of a permanently excited DC motor in the form of a bar-wound armature motor which forms a structural unit with a gear and an electronic control unit. A tongue-like projection of the control unit has, at its free end, means for making electric contact with the motor and Hall-effect sensors associated with a ring magnet arranged on the motor shaft. The adjusted position of the windowpane as well as the adjustment rate can be determined from the sensor signals. If an object is trapped in the closing window gap, the resistance to adjustment increases so the interval between the succeeding signals increases. If a previously defined extent of change in speed is exceeded, the drive is stopped and the windowpane reversed.
A corresponding method of trap protection for controlling a window regulator drive is described in DE 30 34 118 C2. In that patent, the distance covered is determined electronically during the opening and closing process and the opening distance is compared with the respectively covered closing distance during the closing process. The adjustment range of the windowpane is divided into three ranges. In a first range between completely opened and about half opened, the electronic trap protection remains switched off; when a blocked state occurs, the motor is switched off after exceeding a predetermined time limit. In the following second range which ends just before the seal of the window frame, the trap protection is activated. Measured values dependent on the speed or velocity of the unit are determined here and compared with a limit based on the initial measured value. If the limit is exceeded, the controller momentarily changes over the drive and then switches it off. The trap protection is deactivated again when the closure range is reached as the windowpane could not otherwise be completely closed owing to the additional resistance of the seal.
An inadmissibly high trapping force could occur during entrapment owing to the system-dependent motor characteristic which leads to an increase in the torque during a reduction in the motor speed.
To detect entrapment, an adjusting path of the motor shaft carrying the ring magnets which is sufficient for detecting at least one further signal period after the beginning of the entrapment, the signal period being compared with the value for the preceding signal period, is required so an adjustment path of at least two signal periods must be guaranteed. Under undesirable circumstances, in particular when a hard object (for example a head) is trapped, the situation where even the maximum torque is achieved can be a considerable and may not be prevented.
It is accordingly the object of the invention to provide a drive unit for adjusting devices in motor vehicles and to develop a method of controlling the drive unit which are capable of ensuring simple and reliable operation of the adjustment members. In particular, reliable detection of the trap protection and adherence to predetermined limits for the permitted trapping force are to be guaranteed even during speed control for achieving a constant adjustment speed of the adjustment member which is independent of load. In addition, a reliable approach to stop positions should be possible, without additionally distorting the adjustment system with considerable excess forces.
A sealing element which subdivides the motor into a dry space comprising the electric and electronic components and a wet space, is accordingly arranged between the stator and the rotor of the motor drive unit constructed as a synchronous motor. The conditions for the use of inexpensive designs of dry space for the electric components are therefore met. In addition, the best conditions are provided owing to the use of a synchronous motor with its system-specific properties for fulfilling the specific requirements of adjusting devices in motor vehicles. This applies, in particular, to the attainment of a constant speed of adjustment of an adjustment member as the adjustment force requirements change over the adjustment path (for example owing to varying coefficients of friction) and with respect to the compliance with comparatively low trapping forces, particularly if malfunctioning of the trap protection (for example due to vibrations or impacts during travel) is to be avoided.
To guarantee suitable starting conditions, a synchronous motor with at least two windings is used to produce at least two pairs of poles of the rotating field of which the motor speed may be controlled to a constant value via the frequency of the rotating field. The torque proposed for the adjustment movement of the adjustment member is provided via the setting of the load angle xcex4 which is defined as phase displacement between the exciting field and the rotating field of the motor.
Preferably, the stator of the synchronous motor forms a prefabricated, pre-testable unit with the electronic control device and the connectors and optionally with the sensor device. A mechanical carrier comprises interconnecting elements which, for producing a mechanical connection to the stator, engage in the interstices thereof. To protect the electric parts of the stator from moisture, the carrier may be pot-shaped in construction so the stator is at least partially surrounded by the carrier in such a way that the carrier can act as a partition between a wet and a dry space. In this embodiment, the partition extends in the air gap between stator and rotor.
A further method of connecting the stator to the carrier and protecting it from wetness is to fasten the stator on the carrier by encapsulating the stator with a plastics material. If the carrier also consists of plastics material, the stator can be injection moulded into it. To avoid power losses, it is necessary to keep the air gap between stator and rotor as small as possible. Encapsulation of the stator which is as thin-walled as possible should therefore be provided.
The invention is particularly suitable for use in window regulators or sliding roofs, particularly if the body compartment in which the drive unit is arranged has separate wet and dry spaces. Trap protection can be detected simply and particularly reliably. as an adjustment movement of the adjustment member is not required for this purpose. Analysis of the load-dependent phase displacement between the exciting field of the rotor and the rotating field of the stator guarantees, at all times, a reliable measurement which, in conjunction with other measured values such as the adjustment position, adjustment speed and historic measured values, allows complex evaluation. If a specific excess force or maximum trapping force is predetermined, the exceeding of this force can be reliably avoided by adjusting the operating point of the synchronous motor to such a load angle xcex4B before the load angle xcex4K of the breakdown torque that the increase in torque xcex94M between the two load angles xcex4B, xcex4K at the adjustment member (for example windowpane) leads, to the maximum extent, to attainment of a predetermined excess or trapping force.
It is mentioned at this point that the drive according to the invention can also be used to operate seat adjusters. Similarly to window regulators, seat adjusters may be equipped with trap protection to avoid injury. As the conditions for adjusting a vehicle seat depend not only on the operating temperature, the degree of aging, the contamination etc., but also on the weight of the user, it is advisable to adjust each seat quickly and almost unnoticeably before (for example when releasing the vehicle lock) and after the occupation thereof in order to determine the prevailing constraints. The operating point can then be set according to the predetermined requirements.
One of the main requirements in adjusting devices in motor vehicles is uniform running of the drive which is a prerequisite for avoiding modulating noises. For this purpose, the speed of adjustment of the adjustment member is controlled to a constant value via the frequency of the rotating field. The torque provided for the adjustment movement of the adjustment part is set via the load angle xcex4 which is defined as phase displacement between the exciting field and the rotating field of the motor. With varying loading of the adjustment system, the changing load angle xcex4 is kept constant by readjusting the current. This can be effected by pulse width modulation or by a variable resistor.
There are various methods of trap protection or of approaching a stop limiting the adjustment path, the main ones of which will be described in brief hereinafter:
Method of Control With Trap Protection
The prevailing load angle xcex4n is initially measured and the maximum permitted load angle xcex4max of the subsequent phase calculated on the basis thereof, the prevailing load angle xcex4n being increased by a relative value (X%xc3x97xcex4n) or an absolute value (Y degrees). A load angle xcex4n+1 is then measured at a subsequent phase n+1. The load angles xcex4n and xcex4n+1 are now compared with one another. If the deviation is smaller than the value permitted on the basis of the increase (deviation between the maximum permitted load angle xcex4max and the prevailing load angle xcex4n), there is no entrapment and the drive unit will continue to operate by permitting readjustment of the current. However, if the deviation is greater than the value permitted on the basis of the increase, further operation of the drive unit is permitted if the current is not readjusted.
If the exceeding of the breakdown torque of the motor is detected (which is achieved at a load angle xcex4K=180xc2x0/Nwind, Nwind corresponding to the number of motor windings) leading to a stoppage of the motor, an entrapment is assumed. The motor is then switched off; its direction of rotation is reversed; or it continues to operate for a specific time or number of starting cycles, the motor being started up again in accordance with a proposed starting sequence control after each exceeding of the breakdown torque, and on attainment of the predetermined time or number of starting cycles, an entrapment is assumed and the motor is switched off or its direction of rotation reversed.
If, after the exceeding of the breakdown torque within the predetermined time or number of starting cycles with a current adjusted for the load angle xcex4n, a load angle xcex4n+m is measured which is lower than the value permitted on the basis of the increase, a temporary disturbance not based on an entrapment is assumed, so the motor can still be operated. If a load angle is measured that is greater than the value permitted on the basis of the increase, then a continuation of the disturbance is assumed and the motor is switched off or its direction of rotation reversed once the predetermined time has been exceeded.
Method of Control for Approaching a Stop
(A) A normalizing run with an established maximum torque which guarantees reliable attainment of the stop position should first be carried out. The process involves at least measuring and storing the position at which the motor stalls. The next approach of the stop position takes place from an established adjustment position in the vicinity of the stop position at a greatly reduced speed of adjustment and a reduced torque, the torque being controlled by setting the current.
The drive unit is switched off on reaching the stored stop position or on reaching a predetermined maximum torque which is lower than the maximum torque of the normalizing run when the corresponding adjustment position does not exceed a permitted distance from the stored stop position, or on reaching an adjustment position located in front of the stored stop position optionally utilising the slowing-down behaviour of the adjustment system.
(B) A further variation is also based on performance of a normalizing run with an established maximum torque and measurement and storage of the load angle xcex4nxe2x88x921 dependent on the adjustment position of the adjustment member at least for a region directly adjoining the stop position, in order to determine the extent of the position-dependent sluggishness. When the stop position is next approached, the prevailing position-dependent measured values of the load angle xcex4n are detected and stored. The maximum torque to be adjusted is now calculated as a function of the prevailing load angle xcex4n and the load angle xcex4nxe2x88x921 of the preceding adjustment movement. Operation of the drive unit with a torque which is lower than the calculated maximum torque to be adjusted guarantees a mode of operation which protects the system.
It may be sufficient for various applications, however, if the rotating field frequency and the electric current are reduced for approaching a stop position. The drive unit is switched off when the thus reduced breakdown torque is exceeded. It is obviously also possible to switch off the drive unit just before the stop position is reached, thus avoiding additional distortion of the system.
As very low trapping forces can be reliably adjusted with the invention without an adjustment path of the adjustment member being required for entrapment detection, the existence of entrapment must not be assumed, for safety reasons, during a stoppage of the motor due to external influences. Therefore, it is quite possible and sensible to start the motor again or repeatedly using a starting sequence control, to check whether it is a transient event which led to stoppage of the motor. A starting sequence control should be used here to minimize the starting time.
It is thus possible to avoid spurious tripping of trap protection, for example due to vertical acceleration forces when passing over a so-called rough track.
A particular advantage can be that the operating point of the motor of each individual adjusting device can easily be set automatically during a normalizing run by means of the electronic control device. This occurs whenever a predetermined permitted deviation is exceeded. The permitted deviation can be obtained, in particular, from the difference between the smallest load angle xcex4min within the monitored range of an adjustment movement and the load angle xcex4K of the breakdown torque at which a torque difference xcex94M is set, which is capable of producing the maximum permitted adjustment force on the adjustment member.